Friction clutch



Oct. 22, 1940. H. NUTT ET AL 2,219,139

FRICTION CLUTCH Filed Jan. 2l, 1939 3 Sheets-Sheet l I /`5 JZ Z. Z.

jig.. 55

H. NUTT El' AL FRICTION CLUTCH Oct. 22, i940.

Filed Jan. 2l, .1.939 3 Sheets-Sheet 2 Qd. 22, 1940. l H NUTT ET AL 2,219,139

FRIGTION CLUTCH Filed Jan. 21, 1959 s sheets-sheet :s

Patented Oct. 22,A 1940 UNIT- ED su'rA'rEs 2,219,139 FRICTION CLUTCH PATE-.NT3 i .Harold Nutt, Chicago, and Richard L. Smirl, Bellwood, Ill., assignors' tn Borg-Warner Corpora.- tion, Chicago, I ll., a corporation of illinois t l Application January 21, 1939, serial No. 252,190`

v18Claims. (Cl. 1923-68) This application relates friction clutches, and

is economical to manufacture.

has as its primary object to provide a clutch that Specifically, the invention, to provide a 5 clutch in whichth'e amountfofspring steel re quiredin the clutch, is reducedtoa minimum without sacrificing the desirable characteristics of the spring mechanism of clutches now in common usage, but,o'r 1 the contrary with an actual improvement therein;`

In this respect, the invention contemplates ythe n provision of an annular type packing spring hav ing characteristics which allow it vto be made much smaller than is possible in the now available ll' annular type vclutch spring, coupled with an increase in the load capacity and, in addition, more desirable deflection rate characteristics; The invention further aims, in this respect, to provide an annular typepacking -spring which lis accommodated within the inner diameter o f the pres-Vv sure plate andserves as aV baille plate as well'asa packing spring.

With respect to the deflection rate cl 1ar acter ,v

istics of the spring, it isaimed to provide an'an. nular type spring of which the deflection curveV has a. negative 'rate throughout thelentire operat'.

ing range, including therange ofjfacing wear,

whereby, for a given load capacity in the engaged position of the clutch, the amount of work which' must be done in releasing the clutch will bel less than for zero or positive rate springs, and whereby the pressure exerted by the spring against the pressure plate of the clutch will increase in response to facingA Wear so as to compensate for the loss of friction dueto the smoothing of the facings and so as'fto compensate for loss of load in the spring due to fatigue. Another object of the inventionis to provide a friction clutch incorporating a'. vnovel and imv 40 proved arrangement of annular type packing spring in a friction clutch sofas to reduce the axial dimensionthereof.

Another object is to. provide, in a friction clutch, a novel arrangement of' cover plate and release levers, wherein the levers are fulcrume'dl directly against the edgesV of apertures in the plate, through which portions of 'the levers extend. One aspect ofthe improvementin this respect is the provision in the cover plate of a v reentrant shoulder portion connecting the rim to the central web of the plate, the lever receiving apertures being formed in this shoulder portion and the levers being disposed largely within the reentrant spacev circumscribed by said'shoulder DOrtion. f

Another objectv of .the invention is toprovide, a novel arrangement for retaining in position a. re leaseleve'r which is fulcrumed bysimple contact )withan edge of. the cover plate. To this end,;the i invention contemplates the employment of a 'bail- '5 shaped tiel element, the ends of which are hooked into the vcover plate and ,thecentral region of which extends across and in' confining contact with the lever. .j

Other objects', theadventages and uses of the 10 invention will become apparent afterY reading the. following vspecification and claims, and after con'- sideration of vthe vdrawings forming apart of lthe specification, wherein:

Fig. 6 is fa lfragmentary rearelevation offaf Aclutch embodying a modified form oftheinvention.

a fragmentary axial sectional viewv thereof.

Fig. 8 is a fragmentary axial sectional View of 30 another modification of the invention.

Fig. 9 is a fragmentary axial sectional View yoi! i another modification of the invention.

Fig. 1 0 is a sectional'view of the packing spring-:1 modified as to cross-sectional shape. f f 35 Fig. 11 i sl a lfragmentary sectional viewof the f l spring, illustrating anotherimodiflcation of cross'-`v sectional shape.V L 'y Fig.v 12 is` a fragmentary sectional view of ther spring embodying another modication of cross- 40 sectional shape.

Fig. 13 isan elevation or the spring. modified as to circumferential continuity. I Fig. 14 is an elevation of the springwith another .modification as to circumferential .conti- 4.154

Fig. 15 is a graph of the deflection rate of the spring. f

The clutch shown in Figs; 6 and- 7, as anillustration of one formV in which the'invention may 50 be embodiedjcomprisesKV a.- conventional driven plate I0,Z which may bemounted in any conven tional manner upon a hub vI I splined onthe driven shaft I2', and having friction facings I3V adapted to be engaged between the friction' face oi' a conventional ily-wheel I4, and the friction face I5 of a pressure plate I6. The pressure plate I6 is, in accordance with conventional practice, enclosed between the fly-wheel and a cover plate, herein referred to generally by the reference numeral I 1. The cover plate I1 is secured in the conventional manner by means of a flange I8, to the fly-wheel.

The cover plate I1 includes a rim portion I9, a central body portion which is depressed axially toward the ily-wheel, .andl a reentrant shoulder portion 2| which connects the rim portion I9 to vthe central body portion 20. The rim'portion I9 may be provided with conventional flattened regions 22 having lanced openings 23 to receive'the driving lugs 24 of the pressure plate I6 whereby; `to establish a driving connectionV between the fly-wheel and the press'ure plate through the medium of the clutch cover in accordance with conventional practice.

The present invention completely eliminates the usual coil type packing springs and utilizes the space formerly occupied by such springs in obtaining a much greater axial compactness than has formerly been possible. The cover plate I1,V

therebetween to'provide ample clearance for the pressure plate I6 in its retractedlposition, indin cated lin dotted lines in Fig. 7. The reentrant space thus provided, (the space circumscribed'by j the reentrant shoulder 2 I) accommodates the release levers 25. s

Instead of the linkage which was formerly provided for fulcruming the levers relative to the cover plate, the levers, according to the present invention, are fulcrumed directly against vthe radial inner edges of openings 2l inthe 'shoulder 2| of' the cover plate. The shoulderv 2| extends at a substantial angle relative" to thev axis of the clutch, which angle preferably is `roughly in the s neighborhood Aof 45, so that the vsquared'edge of lan opening 2l presents, at the plane of contact of the lever 25 therewith, a. knife edge' fulcrum 26 for the lever.l

The radially outer ends of the levers extend through the openings 21 and thus into the in` terior of the cover plate, wherethey engage in notches 28a in lugs 28 formed integrally with the pressure plate. Thus, the invention eliminates the linkage which is employed in many con-A ventional clutches to connect the outer ends of the levers to the pressure plates, such as, for' example, that embodied in `the less preferred form shown in Fig. 8, wherein the release levers are disposedl entirely outside of the cover plate, and

rconnected tothepressure plate bypull links 29k mounted in the pressure plate, extending through openings 30 in the cover plate Ila, and provided with fulcrum yokes 3l engaging in depressions.

32 in the outer ends of the levers. l

Returning to the form of the invention shown "1n Fig.' '1, the'outer region of the lever 25 which projects through the opening 2'|is inclined ax-f ially toward the ily-wheel as at 40, terminating inl an end portion 4I for reception in the notch 28a of the lug 28, which end portion 4I is disposed in a radial plane substantially intersecting the axis axial depth'of the rim portion I9 tobe restricted so as to extend no further,` rearwardly thanthe plane of the rear extremities of the release levers. The release levers, in turn, being fulcrumed directly against the cover plate, with the fulcrum axes disposed just slightly rearwardly of the rearmost radial plane of the body portion 20, are adapted to utilize substantially all of the available space circumscribed by the shoulder 2|. The central body portion 20 of the cover plate is inclined forwardly` and inwardly as shown, so as to increasingly widen this space toward the center of the clutch in conformity with the increasing range of movement of each portion of the lever progressively further from its fulcrum.

This inclination of the body portion of the cover plate, in addition to providing the proper Y space to accommodate the swinging of the levers,

brings` the inner periphery of the cover plate substantiallyinto the plane of the rear face of the i pressure plate I6, in proper position for engagement with the innerperiphery of the annular packing spring 42, which `is so'constructed and arranged as to add practically nothing to the I axial dimension of the clutch. The outer region of the spring 42 is engagedagainst a reduced thickness central region 43 of the pressure plate, l defined by avshoulder 44 which forms an annular I recess in which the spring is located.

The spring 42 is in Vthe-form ofl a' washer state, shown in Fig. 5, it is roughly frusta-conical,

or J annulus of 'spring sheet metal. `v'In itsunstressed its inner and outer peripheries being spaced axially from eachother sonas 'to define between them an imaginary cone indicated by the broken line C. The spring is dished rearwardly from the imaginary cone C, so that its inner peripheral reginon 451sV substantially tangent to a planeperpendicular tothe axis of rotation; whereas its outer peripheral region 46 is inclined rearwardly and inwardly.

In the ensuing discussion f thecharacteristics K of the spring, reference will bemadefv to the height, crown, and thickness of the spring.

The term height is employed to designate the 'axial dimension between the plane of the axial extremities of the spring, i. e., a plane tangent to the convex side ofthe curved intermediate `region 41 andthe plane Where theperipheral edge Y. of the spring contactsthe pressure plate.

term crown is employed to designate the maximum distance between the imaginary cone C and the concave surface f the intermediate region .41. 1

The

under initial compression so as to bring its inner and outer peripheries closerl together axially, and during clutch release operation, its peripheries will be further deiiected toward va common plane. n

The action of the opposed forces as indicated by the arrows 48y and 49l iiattens `out the imagi-` nary` cone C Vtowarda'radial plane, thus tend.

ingto increase the distance between the outer and inner peripheriesof the, spring as projected upon such radial plane. As a result, the spring is placed under radial compression, theouter peripheral region 46, which tends to increase in diameter, is subjected tocircumferential tension, and the inner peripheral region which tends to contract in diameter, is placed under circumferential' compression. The intermediate region 41- is subjected to a bowing' action as a result of the radial compression.

The radial compression in the spring will vary from a maximum in the intermediate region to a minimum 'at the peripheries, whereas the circumferential stress distribution varies from' a' maximum at the peripheries to aminimum in the intermediate region. It is contemplated that the diameter of greatest radial compression may be made to coincide with the neutral diameter of circumferential stress, by -makingthe crown slightly unsymmetrical, and thereby a stillmore uniform distribution of stress may be obtained. v

In the conventional conical spring, the radial compression in the intermediate region is resisted with practically no deflection,-and causes the peripheral regions to undergo tire major portion of the distortion incidental to deflection.l Increasing the height D of a true cone increases the distortion at the edges, and con-7 sequently increases the stress, which reaches a practical limit at the inner periphery before it does at the outer periphery; because of the greater area of the latter. exceeds the thickness of the spring by more than about 50 per cent., the deflection rate goes from positive to negative and back to positive again, all within the range of customary operating de'- ection.

In the present invention, the intermediater By increasing the curvature of the crown, the rate of the spring, i. e., the ratio of increase of the load to increase in deflection, is increased towardA the positive side. In a truly conical or nearly conical spring, if the height is allowed to exceed a critical point, a very decided and undesirable type of negative rate is developed, wherein the load, beyond a given point of deflection,

will decrease with increased deflection, until` it becomes a negative load and the spring turns inside out and refuses to return to its initial position. Because of this characteristic, it has been necessary in prior springs of the conical type, to restrict the depth, and in so doing the load capacity of the spring has been limited.

The present invention secures a very considerable increase in loadr capacity and at the same time counteracts the tendency toward such an undesirable negative rate, by combining an in` crease in height with the curved or crowned cross-section. This improvement is characteristic of all of the disclosed forms of the invention, including the plain annulus shown in Figs.

1 and 5, circumferentially continuous throughout its entire radius, and the modifications shown in Figs. 13 and 14, which are circumferentially interrupted. While the inventionaims to avoid the undesirable type of negative rate described above, it

does not propose to avoid the negative rate en- Furthermore, if the height tirely. Inl fact, it is an object of the invention to utilize amodied type vof negative rate in order to secure advantages which have 'heretoiore 'been unavailable, so as to decrease the amount of workV which must be done by the oper-` Y ator in releasing the clutch from any given load j at complete engagement.-

In. prior clutches embodying the cone-type 1 spring, substantially zero Vdeilectionrates have been utilized in the 'operating range vof deflection. The deflection curve of such a spring shows` first a positive rate or increase in load during an initial stage ofkdeflection, then a substantially zero, or slightly negative rate, substantially constant or slightly `declining load during an intermediate stage, and again a positive rate during a final stage of deflection. A

disadvantage of such springs has'beenthenarrowness of the range of substantially zero rate.

Because of this, itwas necessary to include within .the'operating range, portions ofthe positive rate deflectionsk in the initial and final stages. The resulting increase in load inr the of clutch'release is objectionable. l

In the present invention, by moderately crowning a spring having the proper proportion of height and thickness, it becomes possible to combine a considerably increased load capacity final stage with a greatly extended range of lnon-positive deflection rate, sufficiently broad to embrace the entire operating range of a clutch plus the range of facing wear. For example, al spring having an overall diameter of approximately 6 inches, a thickness of approximately .095 inch, a` crown of approximately .070 inch, anda height of approximately 135 per cent. more than itsthick'- height of 50 per-scent. more than thickness has been considered critical) displays these desirable characteristics. Such a spring, fatigue-,tested for 500,000 cycles of engagement under` a pre-n load 1240-lbs. stood up without failure.

- ness (as above pointed out, in-'prior springs,r a f In addition to extending the non-positive lrate deflection range of the spring as described above, the invention makesit possible to'selcure a very pronounced negative rate which Adoes not,

however, approach lthe objectionable vzone 'of negativeload characteristic of` conical springs having-too much depth. The pla-in, uninterrupted spring of Fig; l Ygives a moderate negative rate. The negative characteristic can be ldeflnitely increased by interrupting th'e spring at intervals around its circumference in a zoneA occupying a minor portion of its radius, as shown in Figs. 13 and '14, .In one'form of the invention, as shown in Fig. 13, this interruption takes the form lof shared' slits 50, without thickness, formingy a plurality of tongues 52 Which'are in contact with eachother so that the inner region 45 of the spring may be placed under circumferential compression in the initial stage of deflection; .The slits 50 may terminate in openings 5i which serve to preventextension of the slits under the spring.

of the opposed forces 48 and 49, or in its unstressed state as shown at 45a inEig. 10 may be Al Y V bowed toward the plane vof the outer periphery so as to become reentrant as shown for exrepeated deflection of .Y

A' 65 In one of its aspects, the invention contemplates that the inner region 45, under the action ample in Fig. 2, although'inthe preferredform to any appreciable degree, and may, asfshown -of the invention as shown in Fig. 5, in its unv 'stressed state, the inner regionis not reentrant Las stressed state., As the inner region becomes increasinglyreentrant'under deflection, there is an increased tendency to set up circumferential `tension in the inner region as opposed to the circumferential compression which is a resultant of the radial compression, and as a result, a point will be reached` where the compressive force'sare neutraliaed andthe inner region. 45

will be placed under circumferential tension.

The slits 50 prevent fracture of the inner re- .gion 45 under the circumferential tension produced in the final stage of deflection. The slits` 50, `by preventing to a large extent the build-up of Vcircumferential tensionlin the inner region of the final staseof operation, decrease the load required for this` final stage of deflection, and thereby prolong and increase the negative characteristic. During the initial stage of engagementfwhen they are in abutting contact with each other, they tongues 52 have thecharacteristics of a continuous annulus,` whereas in the final stage of deflection they tend to separate from each other and bendl as independent tongues. n .n

In the form shown in Fig. `it, the negative characteristic is increased and `extended as a result of the provision ofa series of openings 5ia in the neutral zone of the annulus. The openings 5|a separate the continuous inner and outer regions 45 and 45 and greatly increase the yieldability of the neutral region to the bowing action.

In the form shown in Fig. 12, the inner region 5b is providedl with a reverse curvev as shown, which tends to counteract the setting up of circumferential tension in the inner region during the ilnal stage of deflection. This also increases and extends the negative characteristic by partially neutralizing the stress in the inner region during the latter stage.

Increasing the "s1ope and extent of the negative portion of the deflection curve (shown in graph form in Fig. 15) is attained inthe present inventionwithout even closely approaching zero or negativeload on the down-swing of the curve. This is made possible by the high load capacity obtained by the curve on its initial upswing indicated at Z. The extension of the negative portion of the curve makes it possible to pre-load the spring Vto a point where its operating range falls entirely within the negative portion of the curve, and in` addition, ample allowance for facing wear may be made so as to maintain the operating range within the negatlve,portion of the curve during the entire life of the driven element of the clutch.

For example, as illustrated in Fig. 15, the spring may be pre-loaded to an initial load of 1350 lbs. as read on the curve Z in connection with the ordinate scale Y, and an initial deflection of .24 inch as read on the curve Z in connection with the abscissa scale X. This point of .pre-loading, representing the fully engaged position of the clutch when new, 'is indicated o n the scale at E, the full released position of the clutch being indicated at `l't,'and the operating range of the clutch when new correspending to that portion of the curve lying between the points E and R.

In arriving at the pre-loading point E, the spring will have followed the curve Z from a starting point O of no deflection and no load to a maximum load of 1430 lbs. at .1B inch deflection, represented at P as the peak of the curve, beyondwhich the amount'of pressure required tok beexerted against the spring in order toproduce further deilectionvhas begun yto decrease. f

Between the peak load point P and the' initial pre-loading point E, there remains` a'jieclining portion of the deflection curve, which may 'be l referred to as the take-up zone, (indicated i atW) vinto which the operating rangewill gradually shift as the facings of the driven member wear down. This results fromgradual lshifting of the pressure plate toward the fly-wheel, al-

k lowing the spring to return toward its unde- The curve shown in 15 `represents the l results of tests on a spring having the charac` teristics shown in Figs. 5 and 13, having a thickness of .095 inch, a height of .267 inch and a crown of .091 inch. Tests on a similar spring,`

differing only in having` a thickness of Y.100

inch and a, depth of .272 inch, gave a maximum loadcapacity of over. 1600 lbs. .when new, and

ilection. y v

Each lever 25 is held against its fulcrum by a bail 33 engaging in a depression 34 in the centr-al reenforcing rib 35 of the lever, and having end trunnions 35 received in openings 31 and 31a in the cover plate, and hooked-behind flap portions 38 upstruck from the cover plate. The opening 31amay be inthe form of a vbayonet slot-having -a portion 3 3 parallel to the bail 33v so as to receive one end trunnion 36 of the :bail

'in order toallow attachment and detachment thereof.k i n ,l

' V'I'he Vend ltrunnions 3,5 when in place beneath the strap portions 33, are axially aligned with the'fulcrum 25, so that the bail 33 may swing withvlthe lever 25 around the fulcrum axis without at any point resisting the free swinging of the lever.

The major portionl of the mas-s of each lever 25 is located rearward-ly of its fulcrum 26. As a result, centrifugal force acting on the -ievers tends to rotate them counter-clockwise as viewed in Fig. 7, causing the outer end regions Il to press against the pressure plate I8 'and .to increase the packing .pressure thereof, with increased speed of rotation.

Thebails 33 hold the levers against their fulcrums iin Opposition 'to the tendency of centrifugal force' to pull the levers away. Being of spring material, the balls will at all times exert a resilient force against the levers. Being thus maintained under constant stress, the bail will not =beapt to break. The tendency of centrifugal force to move the levers 25 bodily outwardly in a radial direction is opposed by shoulders 53,

-of about 1550 lbs. after 250,000 cycles of deformed on the levers 25, which are adapted to Y.

engage against shoulders 54 formed in the cover plate i1 at -the lateral extremitiesI of the opening 21. 'I'he levers are 'located against radially in-l ward movement by fingers 55 which form con- ,tlnuaitions of Ithe shoulders 53, extending axially intoze'ngagement with the inner edge of the openamamonstead of extending the levers l25 through f openings 2lv -in the cover plate, vthe leversmay -be located entirely outside 'of the cover plate shown in Fig. 8. Inthis case, the levers' 25a are Iulcrumed against raised fulcums 51 formedinrthe cover plate Ila, and may be secured against lbodily -outward movement by hooks 58 upstruck the spring 42h, instead of being arranged; withv l its inner periphery in engagementwith Athe cover plate, as in :the .preferred form of the invention,` -is arranged with its inner periphery engaged against ra pressure plate l6b, which may'for this' purpose be extended :further radi-ally'inwardly than in the preferred i'orm of the, invention, and

with its outer periphery engaged against the for- Ward side of a flange 6I forming .the.inner ex` tremity of the cover plate. Aeshoulderl 62, formed adjacent the flange 6I, serves to locate .the spring 42h in properly centered relation. The remainder` of the mechanism may `be the same as in the form of the invention shown in Fig'. 7.

The preferred form of the invention is shown in Figs. 1 and 2. In this form, .the ange 43o of the pressure plate is reducedto minimumthickness so that not only the spring 42, but -a'portion of the central -body portion 20c of thev cover plate, is received within rthe space oircumscrilbed by the shoulder 44o. The release levers 25e are substantially the same in construction as those shown in Fig. ,7, with the exception thatY their intermediate regions `are formed as at 63 to conform to the shape of the reentrant shoulder 27o which in this case is prolonged inwardly beyond o the fulcrum 26o. The ends 4Ic of the levers v25e are provided with semi-cylindrical regions ex extend through openings 65 in flat portions V66 struck inwardly from the rim I9c in a plane perpendicular to the axis of the clutch.

The cover plate Hc is provided with a series of ribs 61 in its central body portion 20c, inter.-

mediate :the levers 25o. The ribs 61 strengthen" and reinforce the cover plate. v

'Ihe bails 33C have rtheir `ends, 36e hooked through e elongated openings 31e and located against depressions 68 in the cover. A bail may be removed by springing oneend to clear its corresponding depression 68 and then sliding-the bail longitudinally until its other end clears the` end of its respective opening 31o; v

In packing the clutches for shipment, itfis desirable to retain the pressure plate and levers within the confines of the periphery of the cover plate I1. This requires compression of the spring 42, and the invention therefore contemplates the employment of retainer bars 69, received in slots 'I0 in outwardly recessed portions 1I of the cover plate |90, and braced by bridging across the side Walls of the recesses. The bars 1U engage lugs l2 projecting from the periphery of the pressure plate IBc, and thereby retain the pressure plate in properly lassembled position until,`in the assembly of the clutch, the cover |90 isE bolted to the fly-wheel I4, whereupon the pressure -plate'i'v will be moved slightly away fromthe bars l0, v removing theiload' from'the'bars and allowing'- them to be readily, removed.

Another fea-turey of improvementfin' "the form` shown in Figs. 1 and A2,' is the piloting of the spring 4 2 bythe engagement of its inner periphery around ya series of spaced lugs'l3'upstruck from the inner region of "the cover -vplate lllcy4 and the provision of clearance spacebetween the outer periphery of the spring 42 and the shoulder 44o. This allows 'for-whatever vexpansion inv diameter of the spring may take place either due to compression or temperature changes' without such expansion'beinginterierred with by the shoulder 44C.

The Shoulders sac, instead o'f-bemg part of th] ngers 55, in this form of `the invention/are formed as the inner edges of a separate pair of fingers 53d, and they engageagainst the exterior surface of offset intermediate portions'Z'ld of the shoulder 2 1c.

The lugs 15, shownA in ings 16 inthe cover i90, are balancinglugs'.

In' the operationof a clutch constructedand the usual manner from the 'clutch pedal' -(not shown). `Forward movement of the' throw-out collar I4 will cause the clutch'levers tolmove` in a counter-clockwise direotionaround their fulcra, therebyl moving the pressure yplate to the right as viewed in Fig. y'7, and flattening the Y Fig. 2,*formed on the*l-v pressure plate l6-c and accessible'throughopenl-V spring 42 between the opposed regions of thekv pressure plate and the cover plate 20. When the pressure on the clutch pedal is released, the spring 42 will react against the cover plateZD and move the pressure plate 4I6 back into engagement with the driven plate i0.-

We claim: -A 1 l. In a friction clutch, a cover plate, apressure plate, .and a clutch packing spring comprising van annulus of spring sheet material, curved in radial cross section, with its inner. and outer edges both lying on thesame side of theplane of its mid-portion, said annulus being interposed between said cover plate and pressure plate with the convex side of its radially inner region in engagementwiththe cover plate and its outer periphery. in engagement with the .pressureplate 2. A clutch spring comprising an annulusv of spring sheet material, roughlyl conicaL. provided in its inner region. witha plurality of radial slitsv opening into. itsfinner marginr and defining a plurality of tongues which are.in'abutting conef tact` with each other at their side edges. e v Y 3. A clutch spring as dened in claim 2,'where.

in saidy vtongues have a -length approximately` one-third the radial cross-sectional :dimension of thespring .e 1 l 4. A clutch spring vas denedofingclaim 2,

crownedl in radial cross section. .Y n

5.`InY a friction clutch for transmitting .rotation from one.` rotating jelement to another, a cover plate, a pressure plate, a driving member,` a

driven Amember adapted to vbe engaged between said driving member and pressure4 plate for respring comprisingan annulusof spring sheet material, interposed vbetween saidcover A plate1 and pressure plate, with its outer peripheral region `ceiving rotation therefrom, and aclutch packing y.

in engagement with said pressure plate and its inner peripheral region in engagement with said cover plate.

6, In a-friction clutch, acentrally apertured cover plate, a pressure plate, and a clutch'packing spring comprising an annulus of spring sheet vmaterial linterposed. between said pressure plate iandcover plate, with its outer peripheral region in engagementwith said pressure plate and its inner' peripheral region having substantially the same internal diameter as, and in engagement with, the inner peripheral region of thecover l plate.

man xiauy shauow 'friction clutch'compiising a 1cover platehaving a rim portion, a centralv web portion and a reentrant shoulder portion`y connecting said rim and web portions, a .pressure plate disposed within the confines of the cover` plate, a Washer type packing spring interposed between the pressure plate and cover plate with.

its inner and outer peripheral regions in engagement, one with the pressure plate and the other withl the cover plate, and a release lever extending through an aperture in said reentrant shoulder portion, fulcrumed against an edge thereof, and having an axial .thrust transmitting connection with said' pressure plate;

8. An axially shallow friction clutch comprising a cover having 4a rim portion, a central web 4portion and a reentrant shoulder portion con-` tral region, a pressure plate disposedwithin the confines of said cover, an annular clutch packing spring having its margins in engagement with said reentrant portion and said pressure plate' respectively and adapted to urge themapart, a release lever extending through an'aperture in said reentrant portion and fulcrumed against an fedge'thereof, and anV axial thrust transmitting connectionbetween said pressure plate and said lever. `V i 10.` An axially shallow friction clutch comprising a cover having a rim portion and a reentrant frusta-conical shoulder portion, a pressure plate disposed within the confines of saidcover, clutch packing spring means interposed between the pressure plate and cover and adapted to kurge them apart, said shoulder portion `having an aperture deningvat the frusto-conical surface of said shoulder portion an axially directed knife edge, a release lever extendingV through said aper-KV ture and fulcrume'dagainst said knife edge, and.Y an axial thrust transmitting connection betwee said pressure plate and said lever. l

11. An axially shallow friction clutch comprising a cover plate having a rim portion, a central web portion and a reentrant shoulder portion connecting said rim and web portions, a pressure plate disposed withinthe connes of' thecover plate, clutch 'packing spring meansinterposed between' thepressure plate and cover plate and adapted to urge vthem apart, a release lever extendinglthrough an aperture in said reentrant shoulder portion and fulcrumed against an edge thereof, `an axial thrust transmitting connection between said lpressure plate and said'lever, and r a bail ofspring' wire engaging said lever opposite s* the fulcrumland having itspre'nds attached to the cover plate, for maintaining the lever in position against the action of centrifugal force.

12. Anfaxially shallow friction clutch comprising a cover lplate having a rim portion, a central web portion and a reentrant shoulderportion connecting said rim and web portions, a pressure plate disposed within the confines of the covery f plate, clutch packing spring means interposed between the pressure plate and cover plate and i adapted to urge themjapart,. al release lever extending through an aperture in'said reentrant shoulder portion and fulcrumed against an' edge thereof, 'an'axial thrust transmitting connection between said'pressure plate and said lever, and,

a bail extending across and engaging said leverl and having its ends pivoted to the cover plate in lsubstantialI valignment with the iulcrum.

1'3. VAnA axially shallowfriction clutch comprising a coverplate having a rim portion,a central'web portion and a reentrant shoulder portion connecting said rim and web portions,

interposed between the pressure plate and cover plate and adapted to urge them apart, a release lever extending through an aperture in said reentrant shoulder portion and fulcrumed against -'a pressure platedisposed withinv the confines of the 'cover plate, clutch packing spring meansl an edge'thereof, and an axial thrusttransmitting i connection between said pressure plate vand said`A lever, said lever being provided with axially projecting hooks in engagement with 'a radially inner edge of the lever receiving aperture tofform the fulcrum.v

14. An vaxially shallow friction clutch comprising a cover plate having a rimv portion, a'

central yweb portion and a'rreentrant shoulder portion connecting said rim and web portions, a pressure plate disposedy within the connes of the cover plate, clutch packingv spring means interposed between the pressure plate and cover plate and adapted to urge them-"apart, a release lever extending through an aperture in said reentrant shoulder portion and fulcrumed against an edge thereof, and an axial thrust transmitting connection between said-pressure plate and said lever, saidlever being provided with axially projecting hooks in engagement with a radiallyfinner edge of the lever receiving aperture to form the fulcrum, and with circumferentially extend-v ing shoulders 'adapted' to engage a radially outer extremityof said aperture to resist centrifugal force.V l

15. In a friction clutch, a cover'having a rim portion and a'reentrant portion, a pressure plate disposed Within the contines o f the cover, an annularclutch packing spr-ing having its margins in engagement withthe pressure plate and reentrant portion respectively, and a release lever extending through an aperture in'said reentrant portion and fulcrumed against an edge thereof, said lever having its radially outer end in thrust transmitting connection with said pressure plate for urging the latter eithertowardor away from the drivenelement, and'being disposed substantially entirely on one side of the radial plane of its'fulcrum,vwhereby to react to centrifugal force and thereby increase the packing pressure against the pressure plate.

16. In a friction clutch, a driving member, a

pressure plate, a.v driven member adapted to be p margin.

pressure plate, a driven member,andA a packing spring for causing said driven memberv to be .en-f

gaged between said driving member'and pres sure plate, said packing spring being in the form of an annulus, roughly conical, curved in radial `cross-sectionthroughout its entire circumference, I and arranged so that its innerLmargin under n d .efiection approaches the plane of its outer HAROLD l RICHARD L.l A.sii/Imi.. 

